ANNUAL SUMMARY Eastern North Pacific Hurricane Season of 1999
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1036 MONTHLY WEATHER REVIEW VOLUME 132 ANNUAL SUMMARY Eastern North Paci®c Hurricane Season of 1999 JOHN L. BEVEN II AND JAMES L. FRANKLIN Tropical Prediction Center, NWS, NOAA, Miami, Florida (Manuscript received 11 February 2003, in ®nal form 20 October 2003) ABSTRACT The 1999 hurricane season in the eastern North Paci®c is summarized, and individual tropical storms and hurricanes are described. Producing only nine named storms, the season tied 1996 as the second least active on record. Hurricane Dora was the strongest and longest-lived cyclone of the season. Hurricane Greg, the only cyclone to make landfall during the season, weakened to a tropical storm just before moving ashore in Baja California, Mexico. Fifteen deaths resulted from the tropical cyclones. 1. Introduction central Paci®c basin, with Dora later crossing the in- The eastern North Paci®c hurricane basin covers the ternational date line into the western North Paci®c ba- area north of the equator and east of 1408W longitude sin. to Central and North America. Nine tropical storms One can speculate on the reasons for the inactive formed in this basin during the 1999 hurricane season. season. One possibility is the active 1999 Atlantic sea- Of these, six became hurricanes and two became major son (Lawrence et al. 2001), which featured 16 tropical hurricanesÐcategory 3 or higher (maximum sustained cyclones (TCs). Climatologically, most eastern North winds of 97 kt or greater) on the Saf®r±Simpson Hur- Paci®c cyclones can be traced to disturbances (tropical ricane Scale (Simpson 1974); the 1966±98 averages waves) that cross Central America from the Caribbean are 16 tropical storms, 9 hurricanes, and 4 major hur- (Simpson et al. 1969; Avila and Guiney 2000). An ricanes. There were ®ve additional tropical depressions increase in the number of Atlantic storms could po- that failed to reach tropical storm intensity. The 1999 tentially decrease the vigor of waves crossing into the season ties the 1996 season (May®eld and Rappaport Paci®c. Atlantic Hurricanes Cindy, Dennis, Floyd, 1998) for the second least active since satellite obser- Gert, and Jose all formed from tropical waves and then vations began in 1966. Only the 1977 season, with moved out of the Tropics. While tropical waves spawn eight tropical storms (Gunther 1978), was less active. more than one TC occasionally, the remnant wave vor- Table 1 lists the tropical storms and hurricanes of ticity after genesis often appears greatly reduced. A 1999, while Fig. 1 shows a map of their tracks. Most pattern of above-normal activity in the Atlantic cou- of the data used in determining the tracks and inten- pled with below-normal activity in the eastern Paci®c sities (1-min average sustained winds at 10 m) are de- was also noted in 1995, 1996, and 1998. Conversely, rived from satellites; these include Dvorak (1984) in- the active 1997 season in the eastern Paci®c was ac- tensity estimates, cloud-drift winds, and ocean surface companied by a below-normal number of Atlantic sys- scatterometer data (e.g., Tsai et al. 2000). Other sources tems. This inverse relationship is intriguing, but does of data include infrequent surface, upper-air, and radar not occur every year, as noted by Lander and Guard observations. There were no reconnaissance ¯ights into (1998). eastern North Paci®c tropical cyclones in 1999. All 1999 eastern Paci®c tropical cyclones (including Hurricane Greg, which crossed the southern tip of the nondeveloping tropical depressions) could be as- Baja California, Mexico, as a tropical storm on 7 Sep- sociated with Atlantic tropical waves that crossed Cen- tember, was the only storm to make landfall in 1999. tral America. However, the background monsoonlike Hurricanes Dora and Eugene crossed 1408W into the environment may have played a role in the develop- ment of several cyclones. In some cases, the wave de- Corresponding author address: Dr. John L. Beven II, National veloped into a tropical cyclone upon entering the fa- Hurricane Center, 11691 SW 17th Street, Miami, FL 33165-2149. vorable background environment. In other cases, the E-mail: [email protected] wave may have assisted the development of a preex- Unauthenticated | Downloaded 10/04/21 11:24 AM UTC APRIL 2004 ANNUAL SUMMARY 1037 TABLE 1. Eastern Paci®c tropical storms and hurricanes of 1999. Max 1-min Min sea level Name Class* Dates** wind speed (kt) pressure (mb) Deaths Adrian H 18±22 Jun 85 973 6 Beatriz H 9±17 Jul 105 955 Calvin T 25±27 Jul 35 1005 Dora H 6±23 Aug 120 943 Eugene H 6±15 Aug 95 965 Fernanda T 17±22 Aug 55 994 Greg H 5±9 Sep 65 986 9 Hilary H 17±21 Sep 65 987 Irwin T 8±11 Oct 50 997 * T: tropical storm, max sustained winds 34±63 kt. H: hurricane, max sustained winds 64 kt or higher. ** Dates based on UTC and include tropical depression stage. isting monsoon disturbance. Unfortunately, the avail- of 4 and 2, respectively. While the mean ITCZ appears able data often do not allow for a distinction between weak in July (Fig. 3b), monthly low-level wind anom- the two possibilities. alies (not shown) suggest it was close to normal Figure 2 shows an example of a tropical wave cross- strength. Also, 200±850-mb wind shear data (not ing Central America that eventually became Hurricane shown) indicate no obvious inhibiting factors. Thus, Greg. In this particular case, a monsoonlike environ- the reason for the inactive July remains a mystery. ment with some disturbed weather was in place before During August, a well-de®ned mean ITCZ circula- the arrival of the wave. However, tropical cyclogenesis tion was centered southwest of Baja California (Fig. did not occur until the wave arrived. Figure 2 suggests 3c); it also strongly appeared in monthly wind anom- that the tropical cyclogenesis showed better spatial and alies (not shown). Hurricane Eugene and Tropical temporal continuity with the preexisting disturbed Storm Fernanda formed in the vicinity of this feature, weather, which in turn suggests that the wave acted as while Hurricane Dora became a major hurricane in that a trigger for the development of the preexisting mon- area. soon disturbance. During September, the ITCZ shifted northward to Another possible explanation for the reduced activ- near the coast of Mexico east of 1058W (Fig. 3d), cre- ity is that the sea surface temperature (SST) pattern ating a strong cyclonic anomaly along 188±208N from combined with the location of the intertropical con- 1158W eastward into Mexico (not shown). This shift vergence zone (ITCZ) to create a smaller than normal resulted in disturbances passing over or near the moun- area favorable for tropical cyclone formation. Colder tainous areas of southern Mexico, likely limiting cy- than normal SSTs along the equator associated with La clogenesis. Hurricanes Greg and Hilary formed on the NinÄa, combined with the normal cold SSTs generally southeast side of the mean cyclone centered southwest north of 208N, may have limited the area of warm water of Baja California. necessary for tropical cyclone development and main- tenance. This was most notable during August west of 1208W, where only a 108±128-wide east±west band of 2. Tropical storm and hurricane summaries SSTs warmer than 268C existed (not shown). a. Hurricane Adrian: 18±22 June Figure 3 shows monthly mean 850-mb winds for June, July, August, and September 1999. Note the A persistent area of disturbed weather located south month-to-month variation in the location and intensity of the Gulf of Tehuantepec developed a low-level cir- of the ITCZ. During June, the mean position extended culation and convective banding on 16 June. This oc- from Panama west-northwestward to a few hundred curred when a tropical wave, which had moved off the miles southwest of Baja California with mean circu- west coast of Africa 11 days earlier, moved into the lation centers near the western end and just south of preexisting disturbed area. Further development fol- southeastern Mexico. Both circulation centers are lowed, producing a tropical depression about 225 n mi anomalous (not shown). The western center, while ap- southeast of Acapulco, Mexico, near 0600 UTC 18 pearing favorable for TC development, is located near June (Fig. 1). The depression became Tropical Storm cold SSTs. This superposition may have helped sup- Adrian later that day. A deep-layer ridge over Mexico press activity, as any nascent TC in this area would helped steer the cyclone west-northwestward on a track likely have encountered cold water before genesis parallel to the coast of Mexico through 20 June. Adrian could occur. became a hurricane on 20 June and maintained an es- Five tropical cyclones formed in July, which is near timated peak intensity of 85 kt from 1800 UTC 20 normal. However, only 2 of these became storms and June to 0000 UTC 21 June. An eye was brie¯y seen only 1 a hurricane, numbers that are half of the normal in satellite imagery during this time (not shown). Unauthenticated | Downloaded 10/04/21 11:24 AM UTC 1038 MONTHLY WEATHER REVIEW VOLUME 132 . 1. Tracks of eastern Paci®c tropical storms and hurricanes during 1999. IG F Unauthenticated | Downloaded 10/04/21 11:24 AM UTC APRIL 2004 ANNUAL SUMMARY 1039 FIG. 2. Sequence of daily Geostationary Operational Environmental Satellite-8 (GOES 8) infrared satellite images at 1200 UTC from 27 Aug to 4 Sep 1999. Dates are indicated on the right-hand side of the ®gure. Dashed line marks the tropical wave that eventually triggered Hurricane Greg (G). Unauthenticated | Downloaded 10/04/21 11:24 AM UTC 1040 MONTHLY WEATHER REVIEW VOLUME 132 FIG.